1. Field of the Invention
This invention relates to a process for the preparation of 3,5-diamino benzotrifluoride by reduction of 4-chloro-3,5-dinitrobenzotrifluoride. The diamino product of this invention is a valuable chemical intermediate, useful in a variety of organic syntheses. In particular, the diamino product may be employed as a monomer in the preparation of various polymers including polyurethanes and polyimides.
2. Description of the Prior Art
The reduction of aromatic nitro compounds is an important and widely used commercial method for the preparation of aromatic amines. It is known that the nitro group may readily be reduced by various reagents, including iron or tin and hydrochloric acid or sodium sulfide. Catalytic hydrogenation using various hydrogenation catalysts is also known. However, the reduction of aromatic nitro compounds containing ring halogen substituent(s) is unpredictable.
Bouchet, et al., Syn. Commun., 4, 57-9 (1974), disclose the reduction of para-chloronitrobenzene to para-chloroaniline, using hydrogen in the presence of a palladium on carbon catalyst.
According to A. Weizmann (J. Am. Chem. Soc., 71, 4154, 1949)), the catalytic hydrogenation of diethylaminoethyl 4-nitro-2-chlorobenzoate using palladium on barium sulfate as a catalyst was impractical from a preparative point of view. The nitro compound was often incompletely reduced. The chlorine was occasionally removed from the ring while in other reactions it remained on the ring. Similar hydrogenation experiments conducted with 4-nitro-2-chlorobenzoic acid and its ethyl ester, using palladium on barium sulfate as a catalyst, produced variable results depending upon the solvent employed.
British Pat. No. 1457608 discloses processes for reducing nitroaromatic water-insoluble compounds by contacting the compounds with an aqueous solution of a formic acid salt in the presence of a heterogeneous hydrogenation catalyst and a surface active agent, particularly a phase transfer catalyst.
British Pat. No. 1458633 discloses a process for dehalogenating water-immiscible aromatic compounds by contacting the said compound with an aqueous solution of a formic acid salt in the presence of a hydrogenation catalyst and a surface active agent or a phase transfer catalyst.
U.S. Pat. No. 4,792,625 discloses a process for reducing substantially water-insoluble nitroaromatic compounds to the corresponding amine by contacting an aqueous solution of a formic acid salt, e.g., potassium formate, with an organic solution of the nitroaromatic compound in the presence of a hydrogenation catalyst, e.g., palladium on carbon. The process is carried out in a water-insoluble organic solvent such as toluene, benzene, xylene, or preferably an alcohol, e.g., ethanol, propanol, etc.